1. Field of the Invention
The invention relates to a combined mixing and injecting device for introducing feed materials into a mold, more particularly to a device suitable for use in the processing of a foam material, such as a two-part polyurethane foam material.
2. Description of the Related Art
Shoesoles are commonly produced from a two-part type polyurethane foam composition which comprises an isocyanate and a polyol. A typical foam injection device available for introducing a polyurethane foam composition includes a mixer to mix two feed materials, such as the isocyanate and polyol. The resulting mixture is immediately introduced into a preheated mold through an injection port to undergo crosslinking and foaming reactions in the mold. In order to provide the final PU foamed products with the desired characteristics, such as high foam density, good abrasion-resistance, high strength, etc., it is usually necessary to regulate properly the quantity of the two feed materials fed into the mold. Since early injection devices for feeding such a foam material can only produce a single color from one foam composition, more than one foam injection device is required when two or more colors are to be produced from different foam compositions. This increases the cost of manufacture.
In order to address the aforesaid problems, foam injection devices available for injecting different polyurethane compositions and colors are developed by providing a plurality of inlet control devices around a mixer so as to control the delivery of different feed compositions into the mixer. As such, a single foam injection device can serve to feed two or more foam compositions with varying colors into the mixer through different inlet control devices.
FIG. 1 shows a typical foam injection apparatus which includes a mixer (A) and two groups of control systems which are disposed on two sides of the mixer (A) and each of which includes four valve devices 1 connected to a base body 2. Each control system includes a gear 3, a rack 4, four engaging gears 5, an engaging block 6, a front seat 7, screws 8, and a coupling seat 9. The engaging gears 5 are operable to selectively stretch outward so as to engage the gear 3. When the rack 4 is moved downward by operating a hydraulic power unit (not shown), the gear 3 is rotated so that one of the engaging gears 5 in engagement with the gear 3 operates the corresponding valve unit 1 to permit a liquid feed to be injected into the mixer (A). Since the gears 3 in the two control systems operate synchronously, different foam compositions can be injected into the mixer (A) synchronously.
However, although the aforesaid conventional foam injection device can deliver different foam compositions having varying colors, the control systems thereof are complicated and expensive. In addition, the clearances provided between the gears 3 and 5 to facilitate engaging and disengaging operations thereof can cause a lag time in the transmission of motion. Moreover, since the gears 3, 5 tend to wear after a period of use, the two control systems (A) may no longer perform a synchronous operation and the quality of the foamed product will thus become unstable.
A primary object of the present invention is to provide a combined mixing and injection device which is simple and capable of controlling precisely synchronous delivery of two or more feed materials to a mixer, thereby alleviating or minimizing the drawbacks encountered with the aforesaid conventional foam injection device.
Accordingly, a combined mixing and injecting device for mixing and introducing more than one feed material into a mold, comprises a housing having a fluidly sealed pressure chamber divided into upper and lower chambers, a bottom space below the lower chamber, and a wall extending around the pressure chamber and the bottom space. A first plunger is disposed inside the housing and has a top end, which extends into the upper chamber and which has a first piston, and a bottom end which extends into the bottom space and which has a first tapering end face, the first plunger having an axial hole. A second plunger is sleeved around the first plunger and has a top end with a second piston in the lower chamber, and a bottom end with a second tapering end face disposed in the bottom space. The second tapering end face is disposed higher than the first tapering end face. First upper and lower inlet ports are provided in the housing and communicated with the upper chamber respectively above and below the first piston so as to move axially upward or downward the first piston and the first plunger. Second upper and lower inlet ports are provided in the housing and communicated with the lower chamber respectively above and below the second. piston so as to move axially upward or downward the second piston and the second plunger. A shaft passes through the axial hole of the first plunger and extends out of the housing from top and bottom ends of the housing. A mixer is disposed adjacent to the bottom end of the housing and has a mixing chamber. An agitator is disposed inside the mixing chamber and connected to the shaft. A plurality of slide seats are disposed around the housing in an angularly spaced apart relationship and mounted externally and movably on the housing to slide radially, each of the slide seats having an upper portion and a lower portion. A plurality of valve units are mounted radially on the mixer in communication with the mixing chamber and include valve stems respectively connected to the lower portions of the slide seats. A plurality of actuating elements are mounted movably and radially on the wall of the housing and include outer ends to respectively actuate the upper portions of the slide seats, and inner ends extending radially into the bottom space and biased to contact the first and second tapering end faces so as to be cammed thereby for actuating the slide seats and for operating the valve stems.